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2.3.7 Reinforcement Rules
All standards contain regulations for plate structures regarding the size and direction of the reinforcement to be used. For this purpose, the standard classifies the plate structures into certain structural elements. For example, EN 1992-1-1 distinguishes the following structural elements:
- plate (slab)
- wall (diaphragm)
- deep beam
The following graphic illustrates the relation between the user-defined Type of Model, the model for the design, and the structural element type according to the standard, which is used to determine the size and direction of the minimum or maximum reinforcement.
If 3D (see Figure 2.1) is selected as the type of model, the structural component is always designed as a shell, independent of whether both axial forces and moments occur in portions of the structural component, or if there is only one of these internal forces. A model type defined as 2D - XY (uz/φx/φy) is always designed as a plate, while the types 2D - XZ (ux/uy/φy) and 2D - XY (ux/uy/φz) are designed as walls.
After selecting the structural component type, the regulations of the respective standard are automatically used when determining the required reinforcement. We will now briefly look at these regulations for EN 1992-1-1, which distinguishes between solid plates, walls, and deep beams.
For solid plates, EN 1992-1-1 specifies the following:
- Clause 220.127.116.11 (1):
The minimum area of the longitudinal tension reinforcement must normally correspond to As,min.
- Clause 18.104.22.168 (3):
The cross-sectional area of the tension or compression reinforcement may generally not exceed As,max outside of lap locations. The recommended value is 0.04 Ac.
According to DIN EN 1992-1-1/NA:2010, the sum of the tension and compression reinforcement may not exceed As,max = 0.08 ⋅ Ac. This is also true for the lap locations.
For walls, EN 1992-1-1 specifies the following:
- Clause 9.6.2 (1): The area of the vertical reinforcement should be between As,vmin and As,vmax. The recommended values are As,vmin = 0.002 ⋅ Ac and As,vmax = 0.04 ⋅ Ac outside the lap locations.
- DIN EN 1992-1-1/NA:2010 specifies
- generally: As,vmin = 0.15 ∣ NEd ∣ ÷ fyd ≥ 0.0015 ⋅ Ac
- As,vmax = 0.04 ⋅ Ac (this value may be doubled in laps)
- The reinforcement content should be equal at both wall faces.
- Clause 9.6.3 (1):
A horizontal reinforcement that runs parallel to the faces of the wall (and to the free edges) should ordinarily be provided at the outer face.
Generally, it must not be less than As,hmin.
The recommended value is the greater value between 25 % of the vertical reinforcement and 0.001 ⋅ Ac.
DIN EN 1992-1-1/NA:2010 specifies
- generally: As,hmin = 0.20 ⋅ As,v
- The diameter of the horizontal reinforcement must be at least a quarter of the diameter of the perpendicular members.
According to EN 1992-1-1, clause 5.3.1 (3), a beam is considered to be a deep beam if the component's span is less than three times the cross-section depth. In this case, the following applies:
- Clause 9.7 (1): Deep beams should normally be provided with an orthogonal reinforcement mesh with a minimum area of As,dbmin near each face. The recommended value is 0.001 ⋅ Ac, but not less than 150 mm2/m per face and direction.
DIN EN 1992-1-1/NA:2010 specifies
- As,dbmin = 0.075 % of Ac ≥ 150 mm2/m
In addition to the normative and therefore unalterable reinforcement specifications, you can specify your own reinforcement rules. These minimum reinforcements can be specified in the Reinforcement Ratios tab of window 1.4 Reinforcement.
For example, if a minimum secondary reinforcement of 20 % of the largest provided longitudinal reinforcement is specified, the [Calculation] first determines the maximum longitudinal reinforcement. In the results windows, this is shown as the Required Reinforcement.
You can check the minimum secondary reinforcement by clicking the [Design details] button.
In the example above, the Secondary Reinforcement into Direction 2 is 20 % of the reinforcement provided in reinforcement direction 1 (here main direction): 7.76 cm2/m ⋅ 0.2 = 1.55 cm2/m. Since this value is greater than the Governing longitudinal reinforcement into direction 2 with 1.35 cm2/m, the secondary reinforcement is decisive.